Get your robot.txt file and inspect it for any changes.
Check your index count in google by using the site: search operator. Compare this to the number of pages you actually have.
If there’s a huge gap, you may be dealing with an index bloat problem due to faceted navigation issues.
Go into search console, check your site map,Take your urls and plug them into the url inspector. See if they are indexed in google by testing the live url.
Check the live url reports and you’ll find out if there are canonical issues
check your coverage reports and look for the excluded urls, error trends.